1. Field of the Invention
The present invention relates in general to an apparatus for detecting an abnormal condition of a motor. In particular, the invention relates to an apparatus for detecting an abnormal condition of a motor in an electric power steering apparatus in which steering torque generated in a shaft due to the operation by a driver is assisted with a motor.
2. Description of the Related Art
FIG. 16 is a block diagram showing a configuration of a conventional apparatus for detecting an abnormal condition of a motor for use in an electric power steering apparatus. The configuration of the conventional apparatus for detecting an abnormal condition of a motor will be described hereinafter with reference to FIG. 16.
In FIG. 16, reference numeral 1 designates a steering torque detector connected to a steering torque sensor mounted to a steering column shaft (not shown), and reference numeral 6 designates a phase compensator for, in response to an output signal from the steering torque detector 1, compensating for its phase.
In addition, reference numeral 13 designates a vehicle speed detector connected to a sensor for detecting the rotation and the like of a vehicle shaft (not shown) to output a vehicle speed signal, and reference numeral 2 designates a steering torque controller for determining a necessary steering torque in response to both an output signal of the phase compensator 6 and an output signal of the vehicle speed detector 13.
Reference numeral 5 designates a motor current determining unit for determining a current value of a motor required to generate the torque value determined by the steering torque controller 2, reference numeral 3 designates a current feedback controller including an adder-subtractor 11, reference numeral 7 designates a motor driver, reference numeral 8 designates a driving motor of the power steering apparatus, and reference numeral 9 designates a motor current detector for detecting a current value of the motor 8 to negatively feedback the detected current value to the adder-subtractor 11.
Next, the description will be given hereinafter with respect to the operation of the conventional apparatus for detecting an abnormal condition of a motor having the above-mentioned configuration for use in the electric power steering apparatus.
First of all, upon detection of the torque of a steering wheel by the steering torque detector 1, the phase compensator 6 compensates for the phase delay of the torque detected by the steering torque detector 1 to input its output signal to the steering torque controller 2. Also, the vehicle speed signal detected by the vehicle speed detector 13 is inputted to the steering torque controller 2. Then, the steering torque controller 2, on the basis of both the input signals, determines a torque value used to assist the steering torque generated by a driver through the operation of a steering wheel.
Then, the steering torque controller 2 inputs the torque value to be assisted to the motor current determining unit 5 to determine a target current. The adder 10, on the basis of the target current, adds an output signal of the current feed forward controller 4 and an output signal of the current feedback controller 3 to each other. Then, a signal which is obtained by integrating an output signal of the adder 10 and a battery voltage in an integrator 12 is inputted to the motor driver 7 to carry out the control so that an output torque of the motor 8 becomes a desired torque.
In addition, the current flowing through a coil of the motor 8 is detected in the form of an actual current value by the motor current detector 9 to be fed back to the feedback controller 3 through the adder-subtractor 11.
With the configuration as described above, for the detection of an abnormal condition of a motor, heretofore, as described in JP 2001-310750 A for example, an abnormal condition is detected on the basis of a difference between a target voltage and an actually measured voltage developed across motor terminals by the motor abnormality detector 15.
In addition, with the technique described in JP 8-310416 A, an abnormal condition of a motor is detected on the basis of a difference between a target current and a detected motor current.
However, there is encountered a problem in that when a disturbance voltage is generated between a target voltage or a voltage developed across motor terminals and a voltage actually applied to a motor coil, this disturbance voltage can not be directly detected.
In the light of the foregoing, an apparatus for detecting an abnormal condition of a motor according to the present invention has been made in order to solve the above-mentioned problems associated with the prior art, and it is, therefore, an object of the present invention to estimate a disturbance voltage (an abnormal voltage value caused by the influence of a disturbance voltage due to breakage, abrasion and flaws of a commutator and brushes of a motor, or a foreign object got mixed into the inside of a motor, broken pieces of internal components or parts of a motor, or the like for example) from a difference between a target voltage and an actual current of a motor to thereby judge an abnormal state of a motor due to the influence of such a disturbance voltage without adding hardware.
According to the present invention, there is provided an apparatus for detecting an abnormal condition of an electric motor, including:
motor current detecting means for detecting an actual current caused to flow through the motor;
feedback controlling means for feedback-controlling a target voltage value that gives the motor a driving command in accordance with the deviation of the actual current from an inputted target current;
abnormal voltage estimating means for on the basis of the target voltage and the actual current, estimating an abnormal voltage estimation value corresponding to a voltage exhibiting an abnormal condition caused in the motor;
commutation frequency arithmetically operating means for arithmetically operating a commutation frequency on the basis of a rotational speed of the motor, and the number of commutators and the number of brushes of the motor;
a filter device for changing a filter frequency in accordance with the commutation frequency to filter the abnormal voltage estimation value estimated by the abnormal voltage estimating means; and
motor abnormality judging means for judging an abnormal condition of the motor on the basis of the comparison of the abnormal voltage estimation value filtered by the filter device with a predetermined abnormal voltage value previously stored.